Prevalence of Autism Spectrum Disorder in a Japanese Community-Based Population Sample of Five-Year-Old Children

Background: In Japan, local governments perform pregnant women and infants’ health check-up as a fundamental maternal-and-child-health service. However, it cannot completely pick up developmental disabilities, especially ASD. A further problem is that the children with ASD who were undetected by the checkup tend to show secondary problems because of maladjustment after entering a school. Psychiatric disorders are common and frequently multiple in children with ASDs (Simonoff, 2008). Therefore, we conducted five-year-olds developmental health check-up on about 1,300 children per a year in a local city, where the number of citizens is approximately 180,000, and directly diagnosed developmental disorders. It allows investigating the prevalence of ASD, and proposing early identification and intervention.  

Objectives: The purpose of this study is to investigate the prevalence of Autism Spectrum Disorder (ASD) in a community-based population sample of five-year-old children. We also clarify the difference of clinical data between children with ASD or other developmental disorders and healthy controls. 

Methods: This study was conducted as Hirosaki Five years check-up (HFC) study-assessing mental health among children in Hirosaki. Subjects are 1919/2571 children who become 5 year old between April 2013 and March 2015 in Hirosaki city. After primary screening was performed, 405 children were selected to undergo secondly developmental health examination. Finally 282 children and their parents visited to the developmental health check-up. Pediatricians and psychiatrists diagnosed neurodevelopmental disorder directly using DSM-5 criteria, ASD, ADHD, DCD (Developmental coordination disorder), and ID/BID (Borderline Intellectual Disability). We calculated the prevalence and comorbidities. In addition, clinical data were statistically analyzed by multiple comparisons with Bonferroni correlation between groups of ASD (comorbid with other disorders), other developmental disorders and healthy control.

Results: 59 children were diagnosed as ASD. The prevalence of ASD was 3.31% (95% CI: 2.48 –4.14). The comorbidities of ASD were ADHD (55.9%), DCD (59.3%) and ID/BID (44.1%). 46/88 ADHDs were ADHD without any comorbidity. 43/59 ASDs (73%) had not been diagnosed with ASD until this health checkup. Mean birth weight of ASDs was significantly lower than other developmental disorders and control groups. In mean CSHQ (Children’s Sleep Habit Questions) scores, Bedtime Resistance of ASDs was significantly higher than other groups. In mean Conners3 scores, ‘Anxiety’ of ASDs was significantly higher than other groups. In mean the child side scores of PSI (Parenting Stress Index) , ASD group was significantly higher than other groups.

Conclusions: This is the first epidemiological study of a community-based population sample in Japan. These findings suggest that ASD children and their caregivers have more difficulties than other developmental disorders and healthy children and 40% of them have not yet received any support.